How to render in cycles volume with camera inside
Update

Camera in volume is now natively supported as of 2.73:


  Cycles: Add support for cameras inside volume
  
  Basically the title says it all, volume stack initialization now is
  aware that camera might be inside of the volume. This gives quite
  noticeable render time regressions in cases camera is in the volume
  (didn't measure them yet) because this requires quite a few of
  ray-casting per camera ray in order to check which objects we're
  inside. Not quite sure if this might be optimized.
  
  But the good thing is that we can do quite a good job on detecting
  whether camera is outside of any of the volumes and in this case there
  should be no time penalty at all (apart from some extra checks during
  the sync state).
  
  For now we're only doing rather simple AABB checks between the
  viewplane and volume objects. This could give some false-positives,
  but this should be good starting point.
  
  Need to mention panoramic cameras here, for them it's only check for
  whether there are volumes in the scene, which would lead to speed
  regressions even if the camera is outside of the volumes. Would need
  to figure out proper check for such cameras.
  
  There are still quite a few of TODOs in the code, but the patch is
  good enough to start playing around with it checking whether there are
  some obvious mistakes somewhere.
  
  Currently the feature is only available in the Experimental feature
  sey, need to solve some of the TODOs and look into making things
  faster before considering the feature is ready for the official
  feature set. This would still likely happen in current release cycle.




As user sambler pointed out, fix is on the way.